The present invention relates to a stitched multiaxial reinforcing laminate composed of carbon fiber yarns, in more detail, a stitched multiaxial reinforcing laminate having a thin thickness composed of thick tow-like carbon fiber yarns, a fiber-reinforced plastic using the same, and a production process of the stitched multiaxial reinforcing laminate.
Carbon fibers have a low specific gravity, high tensile strength and high tensile modulus of elasticity, and carbon fiber reinforced plastics obtained by immobilizing them with a resin (hereinafter called CFRP) are materials having high specific strengths and high specific moduli. The materials are popularly used as component materials of spacecraft, aircraft and sports and leisure articles, and recently, their use for general industrial applications such as motor vehicles is actively studied.
A conventional CFRP is produced, for example, by a method of impregnating a woven fabric with a unit weight of 200 to 300 g/m2 formed using thin carbon fiber yarns with a fineness of 200 Tex as warp and weft, with a resin, to make a prepreg, laminating plural sheets of the prepreg, and forming the laminate in an autoclave.
Since the conventional CFRP is composed of thin carbon fiber yarns, the carbon fibers are very uniformly dispersed in the CFRP, and the surface of the CFRP is smooth. However, thin carbon fiber yarns are expensive since their productivity is low. The woven fabric composed of them is also low in productivity since it must be produced using numerous carbon fiber yarns. So, the production cost of the woven fabric is high, and the conventional CFRP produced using the woven fabric is a very expensive material disadvantageously.
If the CFRP is isotropic, the strength and other properties can be further improved. For this reason, in the case where at least four sheets of a prepreg are laminated, they are laminated to have carbon fiber yarn intersecting angles of 0xc2x0/90xc2x0/xc2x145xc2x0, and this method is called a pseudo-isotropic lamination method. In this case, as the sheets of the prepreg used for the xc2x145xc2x0 layers are obtained by bias-cutting the prepreg used for the 0xc2x0 and 90xc2x0 layers. In addition to the necessity of this cutting step, the cutting involves a large loss of the prepreg. So, the pseudo-isotropic CFRP obtained like this has a problem of being expensive.
Even such an expensive material can be used for the aircraft because of the large weight reduction effect obtained. However, the recently examined CFRP expected for general industrial applications such as motor vehicles is requested to be lower in price. That is, the CFRP available for general industrial applications must be able to be produced at a low cost as an essential condition.
As a means for solving the problem, the use of a stitched multiaxial laminate obtained by stitching pseudo-isotropically laminated reinforcing fibers integrally by means of stitching threads attracts attention. Since the laminate is pseudo-isotropic already as one board, neither bias cutting work nor additional lamination work is necessary. In this sense, the laminate is expected as a low cost material.
In the stitched multiaxial laminate, plural sheets, each having numerous thin reinforcing fiber yarns arranged in one direction, are laminated and stitched integrally by means of stitching threads. In the case where the stitched multiaxial laminate is used as a material for CFRP, the unit weight of reinforcing fibers of each sheet must be about 200 g/m2. However, in the case where carbon fibers are used as reinforcing fibers of the stitched multiaxial laminate, since the production cost of thin carbon fiber yarns is very high, the stitched multiaxial laminate obtained becomes expensive and cannot be used for general industrial applications disadvantageously.
If it is attempted to use thick carbon fiber yarns low in production cost for obtaining a stitched multiaxial laminate with fibers dispersed uniformly, the laminate has a high unit weight and cannot be used for other than special applications. If it is attempted to obtain a laminate with a practical unit weight, the pitch of the arranged numerous carbon fiber yarns becomes large, and a problem arises that large gaps are formed between the respectively adjacent carbon fiber yarns. If the laminate is used for forming a CFRP, the gaps in the formed CFRP become resin-rich portions, and a problem arises that when a stress acts on the CFRP, the stress is concentrated at the resin-rich portions, to cause rupture at a low external force. Furthermore, the shrinkage caused when the resin is hardened depresses the resin-rich portions corresponding to the gaps between the respectively adjacent carbon fiber yarns, and a problem arises that a CFRP with a smooth surface cannot be obtained. Therefore, in the present situations, such a CFRP cannot be used for applications requiring reliability and accuracy.
The object of the invention is to solve the above-mentioned various problems of the prior art by providing a thin stitched multiaxial reinforcing laminate, in which, even if thick tow-like carbon fiber yarns are used, the carbon fiber yarns are uniformly arranged without forming any gap between the respectively adjacent carbon fiber yarns. The object of the invention also includes providing a process for producing the stitched multiaxial laminate.
The stitched multiaxial reinforcing laminate of the invention for achieving the above object is as follows.
A stitched multiaxial reinforcing laminate, in which plural sheets, each having plural tow-like carbon fiber yarns arranged in parallel to each other, are laminated and stitched integrally by means of stitching threads, to ensure that the directions of the arranged carbon fiber yarn of the respective sheets are kept at different angles against a reference direction, characterized in that the tow-like carbon fiber yarns have a fineness of 1,200 to 17,000 Tex respectively and are arranged at a pitch of 8 to 60 mm, with the yarn width of each of the carbon fiber yarns widened to the pitch of the arranged carbon fiber yarns.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the pitch of the arranged carbon fiber yarns is in a range of 20 to 60 mm.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the yarn width of each of the carbon fibers is not less than double the original yarn width. In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the yarn width of each of the carbon fibers is double to five times the original yarn width.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the hook drop value of the carbon fiber yarns is in a range of 4 to 80 cm.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that a sizing agent is added to the carbon fiber yarns, and that the amount of the deposited sizing agent is in a range of 0.2 to 1.5 wt %.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the amount of the deposited sizing agent is in a range of 0.2 to 0.6 wt %.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that the unit weight of the carbon fiber yarns in each of the sheets is in a range of 50 to 300 g/m2.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that said unit weight is in a range of 100 to 200 g/m2.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that at least one sheet of the plural sheets has said carbon fiber yarns arranged substantially at an angle of 0xc2x0 in reference to the direction in which said stitching threads extend, and that at least one sheet of the plural sheets has said carbon fiber yarns arranged substantially at an angle of 90xc2x0 C. in reference to the direction in which said stitching threads extend.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that at least one sheet of the plural sheets has said carbon fiber yarns arranged substantially at an angle of +45xc2x0 in reference to the direction in which said stitching threads extend, and that at least one sheet of the plural sheets has said carbon fiber yarns arranged substantially at an angle of xe2x88x9245xc2x0 in reference to the direction in which said stitching threads extend.
In the stitched multiaxial reinforcing laminate of the invention, it is preferable that said stitched multiaxial laminate contains at least one non-woven fabric layer composed is of reinforcing fibers.
The fiber-reinforced plastic of the invention for achieving the above object comprises a matrix resin and the stitched multiaxial reinforcing laminate of the invention.
The process for producing a stitched multiaxial reinforcing laminate of the invention for achieving the above object is as follows.
A process for producing a stitched multiaxial reinforcing laminate, comprising a carbon fiber yarn-arranging step of arranging plural tow-like carbon fiber yarns respectively having a fineness of 1,200 to 17,000 Tex at a pitch of 8 to 60 mm, with the yarn width of each of the carbon fiber yarns widened to the pitch of the arranged yarns in one direction, a sheet-forming step of forming the arranged carbon fiber yarns into sheets respectively with a carbon fiber yarn unit weight of 50 to 300 g/m2, a sheet-laminating step of laminating the formed plural sheets to ensure that the directions of the arranged carbon fiber yarns of the respective sheets are kept at different angles against a reference direction, and an integrating step of stitching the obtained sheet laminate integrally by means of stitching threads.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the unit weight is in a range of 100 to 200 g/m2.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that, in the carbon fiber yarn-arranging step, the carbon fiber yarns pass along plural width-widening rollers provided in the running direction, to be bent and widened in yarn width.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that at least one of the plural width-widening rollers is a vibrating roller vibrating in the axial direction of the roller, and the carbon fiber yarns passing along it are widened in yarn width by the vibration.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the vibration frequency of the vibrating roller is in a range of 10 to 100 Hz.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that, in is the sheet-forming step, a first width-widening roller device consisting of plural width-widening rollers and a second width-widening roller device consisting of plural width-widening rollers are used, that the numerous carbon fiber yarns arranged at a predetermined pitch are supplied to the first and second width-widening devices in such a manner that every other yarn is supplied to either of the width-widening devices while the remaining every other yarn is supplied to the other width-widening device, that the carbon fiber yarns are widened to wider than the pitch of the yarns arranged when supplied, and that the carbon fiber yarns delivered from the respective width-widening roller devices are positioned adjacently to each other in the formed sheet.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that a fluid is blown to the carbon fiber yarns for widening them in yarn width at a position between the carbon fiber yarn-arranging step and the sheet-forming step.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the fluid is air.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the air is blown from a plurality of blow holes arranged at least in one row in parallel to the orienting direction of the carbon fiber yarns.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the fluid is blown from above a porous guide placed above each of the arranged carbon fiber yarns.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the under surface of the porous guide is kept in contact with the upper surface of the arranged carbon fiber yars.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the yarn width of each of the arranged carbon fiber yarns is not less than double the original yarn width of each of the carbon fiber yarns.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the yarn width of each of the arranged carbon fiber yarns is double to five times the original yarn width of each of the carbon fiber yarns.
In the process for producing a stitched multiaxial reinforcing laminate of the invention, it is preferable that the orienting directions of the carbon fibers in the sheets are at least two angles selected from 0xc2x0, xc2x145xc2x0 and 90xc2x0 in reference to the direction in which the stitching threads extend.